Insulin-like growth factors I and II in healthy man.

Abstract

IGF-I and II share specific serum carrier proteins which elute on neutral Sephadex G-200 gel permeation chromatogrpany at apparent molecular masses of 50 and 200 kD. The half-lives of free and carrier protein-bound 125I-IGF-I and -II were determined after bolus injections of the tracers into two normal adults. Labelled IGF-I and -II migrated first with the 50-kD and later with 200-kD complex. In these complexes their apparent half-lives were 20-30 min and 12-15 h, respectively. The apparent half-life of free 125I-IGF-I and -II was 10-12 min. In a second set of experiments, recombinant human insulin-like growth factor I was infused during 6 days in two healthy adults at a dose 20 .mu.g .cntdot. kg-1 .cntdot. h-1 (corresponding to around 30 mg/day). Serum obtained before and during the infusion was subjected to neutral Sephadex G-200 gel permeation chromatography and fractions were pooled according to the apparent molecular masses at which the carrier protein complexes elute. IGF-I and -II in these pooles were determined by RIA. Before the IGF-I ihnfusion. 92 and 272 .mu.g/l of IGF-I -II were found in the 200 kD complex. 45 and 91 .mu.g 1 in the 50-kD complex, and 15 and 5 .mu.g/l were present in the free form. Corresponding figures during the IGF-I infusion were 389 and 18 .mu.g/l for the 200 kD complex. 201 and 54 .mu.g/l for the 50-kD complex, and 80 < 1 .mu.g 1 for free IGF-I and -II. Using the half-lives of the tracer studies and the levels of the different molecular weight forms of IGF in serum, the production rates for IGF-I and -II were calculated to be 10 mg and 13 mg per day.